functionalized inorganic fluorides · functionalized inorganic fluorides: synthesis,...

FunctionalizedInorganic Fluorides

Synthesis, Characterization & Properties ofNanostructured Solids

Edited by

ALAIN TRESSAUD

Research Director CNRS (Emeritus), ICMCB–CNRS,Bordeaux University, France

A John Wiley and Sons, Ltd., Publication

Functionalized Inorganic Fluorides

FunctionalizedInorganic Fluorides

Synthesis, Characterization & Properties ofNanostructured Solids

Edited by

ALAIN TRESSAUD

Research Director CNRS (Emeritus), ICMCB–CNRS,Bordeaux University, France

A John Wiley and Sons, Ltd., Publication

This edition first published 2010� 2010 John Wiley & Sons, Ltd

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Library of Congress Cataloging-in-Publication Data

Functionalized inorganic fluorides: synthesis, characterization & properties ofnanostructured solids / edited by Alain Tressaud.

p. cm.Includes bibliographical references and index.ISBN 978-0-470-74050-7 (pbk.)1. Fluorides. I. Tressaud, Alain.QD181.F1F77 20105460.731—dc22

2009052139

A catalogue record for this book is available from the British Library.

ISBN: 978-0-470-74050-7 (Cloth)

Set in 10/12pt Times by Integra Software Services Pvt. Ltd., Pondicherry, IndiaPrinted and bound in Great Britain by CPI Antony Rowe, Chippenham, Wiltshire.

Cover images from left to right: Projection along [001] of the ITQ-33 zeolite structure showing the 18-MRswindows (Chapter 16); Schematic morphology of oxyfluoride glass-ceramics formed by spinodal decomposition(Chapter 9); Crystal structure of La2CuO3.6F0.8 [The Cu cations are situated in octahedra; the La cations areshown as large spheres; the F anions are shown as small spheres] (Chapter 13)

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Contents

Preface xvii

List of Contributors xxi

1 Sol-Gel Synthesis of Nano-Scaled Metal Fluorides – Mechanism and

Properties 1

Erhard Kemnitz, Gudrun Scholz and Stephan Rudiger

1.1 Introduction 1

1.1.1 Sol-Gel Syntheses of Oxides – An Intensively Studied and

Widely Used Process 1

1.1.2 Sol-Gel Syntheses of Metal Fluorides – Overview of

Methods 2

1.2 Fluorolytic Sol-Gel Synthesis 4

1.2.1 Mechanism and Properties 5

1.2.2 Insight into Mechanism by Analytical Methods 8

1.2.3 Exploring Properties 27

1.2.4 Possible Fields of Application 29

References 35

2 Microwave-Assisted Route Towards Fluorinated Nanomaterials 39

Damien Dambournet, Alain Demourgues and Alain Tressaud

2.1 Introduction 39

2.2 Introduction to Microwave Synthesis 40

2.2.1 A Brief History 40

2.2.2 Mechanisms to Generate Heat 40

2.2.3 Advantages of Microwave Synthesis 41

2.2.4 Examples of Microwave Experiments 41

2.3 Preparation of Nanosized Metal Fluorides 42

2.3.1 Aluminium-based Fluoride Materials 42

2.3.2 Microwave-assisted Synthesis of Transition Metal

Oxy-Hydroxy-Fluorides 61

2.4 Concluding Remarks 64

Acknowledgements 64

References 65

3 High Surface Area Metal Fluorides as Catalysts 69

Erhard Kemnitz and Stephan Rudiger

3.1 Introduction 69

3.2 High Surface Area Aluminium Fluoride as Catalyst 71

3.3 Host-Guest Metal Fluoride Systems 74

3.4 Hydroxy(oxo)fluorides as Bi-acidic Catalysts 78

3.5 Oxidation Catalysis 84

3.6 Metal Fluoride Supported Noble Metal Catalysts 88

3.6.1 Hydrodechlorination of Monochlorodifluoromethane 90

3.6.2 Hydrodechlorination of Dichloroacetic Acid (DCA) 94

3.6.3 Suzuki Coupling 95

References 97

4 Investigation of Surface Acidity using a Range of Probe Molecules 101

Alexandre Vimont, Marco Daturi and John M. Winfield

4.1 Introduction 101

4.1.1 Setting the Scene: Metal Fluorides versus Metal Oxides 102

4.1.2 Some Examples of the Application of FTIR Spectroscopy to

the Study of Surface Acidity in Metal Oxides 103

4.1.3 A Preview 107

4.2 Characterization of Acidity on a Surface: Contrasts with Molecular

Fluorides 108

4.2.1 Molecular Brønsted and Molecular Lewis Acids 108

4.2.2 A Possible Benchmark for Solid Metal Fluoride, Lewis

Acids: Aluminium Chlorofluoride 109

4.3 Experimental Methodology 110

4.3.1 FTIR Spectroscopy 110

4.3.2 Characteristic Reactions and the Detection of Adsorbed

Species by a Radiotracer Method 112

4.4 Experimental Studies of Surface Acidity 117

4.4.1 Using FTIR Spectroscopy 118

4.4.2 Using HCl as a Probe with Detection via [36Cl]-Labelling 123

4.4.3 Metal Fluoride Surfaces that Contain Surface Hydroxyl

Groups: Aluminium Hydroxy Fluorides with the Hexagonal

Tungsten Bronze Structure 129

4.4.4 Possible Geometries for HCl Adsorbed at Metal Fluoride

Surfaces: Relation to Oxide and Oxyfluoride Surfaces 135

4.5 Conclusions 136

References 137

vi Contents

5 Probing Short and Medium Range Order in Al-based Fluorides using

High Resolution Solid State Nuclear Magnetic Resonance and Parameter

Modelling 141

Christophe Legein, Monique Body, Jean-Yves Buzare,

Charlotte Martineau and Gilles Silly


5.2 High Resolution NMR Techniques 142

5.2.1 Fast MAS and High Magnetic Field 142

5.2.2 27Al NMR 145

5.2.3 High Resolution Correlation NMR Techniques 148

5.3 Application to Functionalized Al-Based Fluorides with Catalytic

Properties 153

5.3.1 Crystalline Aluminium Fluoride Phases 153

5.3.2 19F Isotropic Chemical Shift Scale in Octahedral Aluminium

Environments with Oxygen and Fluorine in the First

Coordination Sphere 153

5.3.3 Fluorinated Aluminas and Zeolites, HS AlF3 157

5.3.4 Aluminium Chlorofluoride and Bromofluoride 158

5.3.5 Pentahedral and Tetrahedral Aluminium Fluoride Species 158

5.3.6 Nanostructured Aluminium Hydroxyfluorides and

Aluminium Fluoride Hydrate with Cationic

Vacancies 159

5.3.7 �iso Scale for 27Al and 19F in Octahedral Aluminium

Environments with Hydroxyl and Fluorine in the First

Coordination Sphere 160

5.4 Alkali and Alkaline-earth Fluoroaluminates: Model Compounds

for Modelling of NMR Parameters 160

5.4.1 19F NMR Line Assignments 161

5.4.2 27Al Site assignments, Structural and Electronic

Characterizations 164

5.5 Conclusion 167

References 168

6 Predictive Modelling of Aluminium Fluoride Surfaces 175

Christine L. Bailey, Sanghamitra Mukhopadhyay, Adrian Wander,

Barry Searle and Nicholas Harrison


6.2 Methodology 176

6.2.1 Density Functional Theory 176

6.2.2 Surface Free Energies 177

6.2.3 Molecular Adsorption 178

6.2.4 Kinetic Monte Carlo Simulations 179

6.3 Geometric Structure of � and �-AlF3 180

6.3.1 Bulk Phases 180

6.3.2 Surfaces 180

Contents vii

6.4 Characterization of AlF3 Surfaces 185

6.5 Surface Composition under Reaction Conditions 188

6.5.1 The �-AlF3–x (01–12) Termination 189

6.5.2 The �-AlF3 (0001) Termination 192

6.6 Characterization of Hydroxylated Surfaces 193

6.7 Surface Catalysis 196

6.7.1 Molecular Adsorption 197

6.7.2 Reaction Mechanisms and Barriers 198

6.7.3 Analysing the Kinetics of the Reaction 200

6.8 Conclusions 201

Acknowledgements 203

References 203

7 Inorganic Fluoride Materials from Solvay Fluor and their Industrial

Applications 205

Placido Garcia Juan, Hans-Walter Swidersky, Thomas Schwarze and

Johannes Eicher


7.2 Hydrogen Fluoride 205

7.2.1 Anhydrous Hydrogen Fluoride, AHF 206

7.2.2 Hydrofluoric Acid 206

7.3 Elemental Fluorine, F2 207

7.3.1 Fluorination of Plastic Fuel Tanks 207

7.3.2 Finishing of Plastic Surfaces 207

7.3.3 F2 Mixtures as CVD-chamber Cleaning Gas 208

7.4 Iodine Pentafluoride, IF5 208

7.5 Sulfur Hexafluoride, SF6 209

7.5.1 SF6 as Insulating Gas for Electrical Equipment 209

7.5.2 SF6 Applications in Metallurgy 209

7.6 Ammonium Bifluoride, NH4HF2 210

7.7 Potassium Fluorometalates, KZnF3 and K2SiF6 210

7.8 Cryolite and Related Hexafluoroaluminates, Na3AlF6, Li3AlF6,

K3AlF6 211

7.9 Potassium Fluoroborate, KBF4 212

7.10 Fluoboric Acid, HBF4 212

7.11 Barium Fluoride, BaF2 213

7.12 Synthetic Calcium Fluoride, CaF2 213

7.13 Sodium Fluoride, NaF 213

7.14 Sodium Bifluoride, NaHF2 213

7.15 Potassium Bifluoride, KHF2 214

7.16 Potassium Fluoroaluminate, KAlF4 214

7.17 Fluoroaluminate Fluxes in Aluminium Brazing 214

7.17.1 Flux Composition 214

7.17.2 Flux and HF 216

7.17.3 Flux Particle Size 217

viii Contents

7.17.4 Flux Melting Range 219

7.17.5 Current Status of Aluminium Brazing Technology 220

7.17.6 Cleaning and Flux Application 221

7.17.7 Wet Flux Application 221

7.17.8 Dry/Electrostatic Flux Application 222

7.17.9 Post Braze Flux Residue 222

7.17.10 Filler Metal Alloys 222

7.17.11 Flux Precoated Brazing Sheet/Components 223

7.17.12 Clad-less Brazing 223

7.17.13 Furnace Conditions 224

7.18 Summary 224

References 225

8 New Nanostructured Fluorocompounds as UV Absorbers 229

Alain Demourgues, Laetitia Sronek and Nicolas Penin


8.2 Synthesis of Tetravalent Ce and Ti-based Oxyfluorides 231

8.2.1 Preparation of Ce-Ca-based Oxyfluorides 231

8.2.2 Preparation of Ti-based Oxyfluorides 232

8.3 Chemical Compositions and Structural Features of Ce and

Ti-based Oxyfluorides 233

8.3.1 Elemental Analysis 233

8.3.2 Magnetic Measurements 233

8.3.3 About the Chemical Composition of Ce1�xCaxO2�x and

Ce1�xCaxO2�x�y/2Fy Series 234

8.3.4 About the Structure and Local Environment of Fluorine in

Ce1�xCaxO2�x�y/2Fy Series 237

8.3.5 Composition and Structure of Ti-based Hydroxyfluoride 252

8.4 UV Shielding Properties of Divided Oxyfluorides 263

8.4.1 The Ce-Ca-based Oxyfluorides Series and UV-shielding

Properties 264

8.4.2 Ti Hydroxyfluoride and UV-shielding Properties 266

8.5 Conclusion 267

Acknowledgement 269

References 269

9 Oxyfluoride Transparent Glass Ceramics 273Michel Mortier and Geraldine Dantelle


9.2 Synthesis 274

9.2.1 Synthesis by Glass Devitrification 275

9.2.2 Transparency 277

9.3 Different Systems 279

9.3.1 Glass-Ceramics with CaF2 as their Crystalline Phase 281

9.3.2 Glass-Ceramics with �-PbF2 as their Crystalline Phase 281

Contents ix

9.3.3 Glass-Ceramics with CdF2/PbF2 as their Crystalline Phase 281

9.3.4 Glass-Ceramics with LaF3 as their Crystalline Phase 282

9.4 Thermal Characterization 282

9.4.1 Kinetics of Phase-change/Devitrification 288

9.4.2 Thakur’s Method 288

9.5 Morphology of the Separated Phases 289

9.6 Optical Properties of Glass-Ceramics 293

9.6.1 Influence of the Devitrification on the Spectroscopic

Properties of Ln3þ 293

9.6.2 Effect of High Local Ln3þ Concentration in Crystallites 295

9.6.3 Comparison of the Optical Properties of Glass-Ceramics and

Single-Crystals 297

9.6.4 Multi-doped Glass-Ceramics 299

9.7 Conclusion 301

References 302

10 Sol-Gel Route to Inorganic Fluoride Nanomaterials with Optical

Properties 307

Shinobu Fujihara


10.2 Principles of a Sol-Gel Method 308

10.2.1 Metal Oxide Materials 308

10.2.2 Metal Fluoride Materials 308

10.3 Fluorinating Reagents and Method of Fluorination 309

10.4 Control of Shapes and Microstructures 313

10.5 Optical Properties 317

10.5.1 Low Refractive Index and Anti-Reflection Effect 317

10.5.2 Luminescence 322

10.6 Concluding Remarks 326

References 326

11 Fluoride Glasses and Planar Optical Waveguides 331

Brigitte Boulard


11.2 Rare Earth in Fluoride Glasses 332

11.2.1 Fundamentals 333

11.2.2 Applications: Laser and Optical Amplifiers 334

11.3 Fabrication of Waveguides: A Review 336

11.4 Performance of Active Waveguides 338

11.4.1 Optical Amplifier 340

11.4.2 Lasers 341

11.5 Fluoride Transparent Glass Ceramics: An Emerging Material 342

11.6 Conclusion 344

References 344

x Contents

12 Polyanion Condensation in Inorganic and Hybrid Fluoroaluminates 347

Karim Adil, Amandine Cadiau, Annie Hemon-Ribaud,

Marc Leblanc and Vincent Maisonneuve


12.2 Synthesis 348

12.3 Extended Finite Polyanions (0D) 350

12.3.1 Isolated AlF4 Tetrahedra 350

12.3.2 Isolated AlF6 Octahedra 350

12.3.3 Al2F11 Dimers 353

12.3.4 Al3F16 Trimers 353

12.3.5 Al2F10 Dimers 353

12.3.6 Al4F20 Tetramers 354

12.3.7 Al4F18 Tetramers 354

12.3.8 Al5F26 Pentamers 355

12.3.9 Al7F30 Heptamers 355

12.3.10 Al8F35 Octamers 356

12.3.11 Mixed Polyanions 356

12.4 1D Networks 358

12.4.1 AlF5 Chains 358

12.4.2 Al2F9 Chains 359

12.4.3 Al7F29 Chains 360

12.4.4 AlF4 Chains 360

12.4.5 Mixed Polyanions and/or Chains 361


12.5.1 Al3F14 Layers 365

12.5.2 AlF4 Layers 365

12.5.3 Al2F7 Layers 366

12.5.4 Al5F17 Layers 366

12.5.5 Al3F10 Layers 368


12.6.1 Al7F33 Network 368

12.6.2 Al2F9 Network 368

12.6.3 AlF3 Network 369

12.7 Evolution of the Condensation of Inorganic Polyanions 372

12.7.1 Influence of Amine and Aluminum Concentrations 372

12.7.2 Temperature 374


Supplementary Materials 376

References 376

13 Synthesis, Structure and Superconducting/Magnetic Properties of

Cu- and Mn-based Oxyfluorides 383

Evgeny V. Antipov and Artem M. Abakumov


13.2 Chemical Aspects of Fluorination of Complex Oxides 384

Contents xi

13.3 Structural Aspects of Fluorination of Complex Cuprates and

Superconducting Properties 388

13.3.1 Electron Doped Superconductors: Heterovalent

Replacement 1O2� ! 1F� 389

13.3.2 Hole Doped Superconductors: Fluorine Insertion into

Vacant Anion Sites 390

13.3.3 Structural Rearrangements in Fluorinated Cuprates 398

13.3.4 Fluorination of Nonsuperconducting Cuprates 408

13.4 Fluorination of Manganites 411

13.5 Conclusions 415

References 416

14 Doping Influence on the Defect Structure and Ionic Conductivity of

Fluorine-containing Phases 423

Elena I. Ardashnikova, Vladimir A. Prituzhalov and Ilya B. Kutsenok


14.2 Influence of Oxygen Ions on Fluoride Properties 427

14.2.1 Pyrohydrolysis 427

14.2.2 Heterovalent Oxygen Substitution for Fluoride Ions 428

14.2.3 Ionic Conductivity of Oxyfluoride 429

14.3 Cation Doping of Fluorides 431

14.3.1 Isovalent Replacement in the Cation Sublattice 431

14.3.2 Heterovalent Replacement in the Cation Sublattice 432

14.4 Active Lone Electron Pair of Cations and Ionic Conductivity 432

14.5 Peculiarities of the Defect Structure of Nonstoichiometric

Fluorite-like Phases 435

14.5.1 Fluorite Structure 435

14.5.2 Defect Clusters 435

14.5.3 Ordered Fluorite-like Phases 439

14.5.4 Phase Diagrams 441

14.6 Ionic Transfer in Fluorite-like Phases 441

14.6.1 Defect Region Model 443

14.6.2 Nonstoichiometric Fluorites as Examples of

Nanostructured Materials 447

14.7 Peculiarities of the Defect Structure of Nonstoichiometric

Tysonite-like Phases 449

14.7.1 Tysonite Structure, Tysonite Modifications and Anion

Defects 449

14.7.2 Ordered Tysonite-like Phases 454

14.8 Ionic Transfer in Tysonite-like Phases 454

14.8.1 Fluoride Ions’ Migration Paths in the LaF3 Structure 455

14.8.2 Temperature Dependences of Ionic Conductivity and

Anion Defect Positions 457

14.8.3 Concentration Dependences of Ionic Conductivity in

Tysonite-like Solid Solutions 459

xii Contents

14.9 Conclusions 462

References 462

15 Hybrid Intercalation Compounds Containing Perfluoroalkyl Groups 469

Yoshiaki Matsuo


15.2 Preparation and Properties of Intercalation Compounds

Containing Perfluoroalkyl Groups 471

15.2.1 Preparation 471

15.2.2 Exfoliation and Film Preparation 475

15.2.3 Introduction of Photofunctional Molecules 476

15.3 Photophysical and Photochemical Properties of Dyes in Intercalation

Compounds Containing Perfluoroalkyl Groups 478

15.3.1 Microenvironment Estimated by using Probe Molecules

Showing Photophysical Responses 478

15.3.2 Photophysical Properties 480

15.3.3 Photochemical Properties 482

15.4 Conclusion and Future Perspectives 484

References 484

16 The Fluoride Route: A Good Opportunity for the Preparation of 2D and

3D Inorganic Microporous Frameworks 489

Jean-Louis Paillaud, Philippe Caullet, Jocelyne Brendle, Angelique

Simon-Masseron and Joel Patarin


16.2 Silica-based Microporous Materials 490

16.3 Germanium-based Microporous Materials 499

16.4 Phosphate-based Microporous Materials 504

16.5 Synthetic Clays 506

16.5.1 Semi-Synthesis 507

16.5.2 Solid State Synthesis 508

16.5.3 Hydrothermal Synthesis 509

16.6 Conclusion 510

References 511

17 Access to Highly Fluorinated Silica by Direct F2 Fluorination 519Alain Demourgues, Emilie Lataste, Etienne Durand and Alain Tressaud


17.2 Mesoporous Silica and Fluorination Procedures 520

17.3 About the Chemical Composition and Morphology of Highly

Fluorinated Silica 521

17.4 FTIR Analysis 523

17.4.1 About the Content and Nature of OH/Water Groups in

Highly Fluorinated Silica 523

Contents xiii

17.4.2 FTIR Bands Related to Si-F Bonds 526

17.4.3 Correlation between Silanol Groups on Mesoporous

Silica and Grafted Fluorine on Highly Fluorinated Silica 527

17.5 Thermal Stability and Water Affinity of Highly Fluorinated Silica 530

17.6 Nuclear Magnetic Resonance (NMR) Investigations 533

17.6.1 Local Environments in Highly Fluorinated Silica through

NMR Experiments 534

17.6.2 Effect of Fluorination on the Nuclei Environments 534

17.7 Conclusions on the F2-gas Fluorination Mechanism of

Mesoporous Silica 540


References 542

18 Preparation and Properties of Rare-earth-Containing Oxide Fluoride

Glasses 545

Susumu Yonezawa, Jae-ho Kim and Masayuki Takashima


18.2 Preparation and Basic Characteristics of Oxide Fluoride Glasses

Containing LnF3 546

18.2.1 Preparation of Oxide Fluoride Glasses Containing LnF3 546

18.2.2 Density and Refractive Index 552

18.2.3 Glass Transition Temperature 553

18.3 Optical and Magnetic Properties of LnF3-BaF2-AlF3-GeO2 (SiO2)

Glasses 555

18.3.1 Optical Properties of HoF3-BaF2-AlF3-GeO2 Glasses 555

18.3.2 Optical Properties of CeF3-BaF2-AlF3-SiO2 Glasses 557

18.3.3 Optical Properties of the Glasses Co-doped with

TbF3 and SmF3 564

18.3.4 Magnetic Property of TbF3 Containing Oxide Fluoride

Glasses 566

18.4 Conclusion 568

References 569

19 Switchable Hydrophobic-hydrophilic Fluorinated Layer for Offset

Processing 571

Alain Tressaud, Christine Labrugere, Etienne Durand


19.2 The Principles of the Lithographic Printing Process 572

19.3 Experimental Part 573

19.3.1 Fluorination by Cold rf Plasmas 573

19.3.2 Wettability Measurements 574

19.3.3 Surface Analyses 574

19.4 Various Types of Surface Modifications using Fluorinated rf Plasmas 575

19.4.1 Reactive Etching of Porous Alumina using CF4-Plasma

Treatment 575

xiv Contents

19.4.2 Switchable Hydrophilic/Hydrophobic Fluorocarbon Layer

Obtained on Porous Alumina using c-C4F8 Plasma

Treatment 578

19.5 Comparison of Surface Modifications of Porous Alumina using

Various Fluorinated Media: CF4, C3F8 and c-C4F8 580

19.6 Conclusion 581


References 582

Index 583

Contents xv

Preface

Fluorides and fluorinated materials affect various aspects of modern life. The strategic

importance of fluoride materials, and the use of adapted fluorination surface treatments,

concern many research fields and applications in areas such as energy production, micro-

electronics and photonics, catalysis, colour pigments, textiles, cosmetics, plastics, domes-

tic wares, automotive technology and building.

Among the issues with which they are concerned [1–4] are:

• the historical importance of fluoride fluxes in the production of metals, in particular

aluminium;

• the critical place of fluorine and fluorides in conversion energy processes – for example

components of Li-ion batteries and fuel cells, enrichment of 235U through uranium

hexafluoride for nuclear energy;

• the etching of silicon wafers for microelectronics;

• the technical revolution of fluoropolymers and fluoride coatings, for example Teflon�

and fluorinated plastics, waterproof clothes, biomaterials for cardiovascular or retinal

surgeries, kitchen wares, and so forth;

• the beneficial influence of fluoride on dental caries;

• the dominant use of fluorinated molecules in agrochemistry and phytosanitary products;

• the dramatic increase of fluorine-containing molecules for medicine and pharmacy, as

efficient imaging products, as dental composites for cariostatic improvement, and so

forth;

• the use of 18F-labelled molecules in positron emission tomography (PET) for early

diagnosis of cancer and Alzheimer’s disease.

In the case of inorganic fluorinated solids, numerous improvements have recently been

achieved through the elaboration and functionalization of the materials on a nanometric

scale. The present book covers several classes of nanostructured and functionalized

inorganic fluorides, oxide-fluorides, hybrids, mesoporous materials and fluorinated oxides

such as silica and alumina. The morphologies concerned range from powders or glass-

ceramics to thin layers and coatings whereas the applications involved include catalysts,

inorganic charges, superconductors, ionic conductors, ultaviolet (UV) absorbers, phos-

phors, materials for integrated optics, and so forth. Several books have been devoted to the

reactivity of carbon-based materials with fluorine (carbon fibres, fullerene, carbon nano-

tubes, etc) [1,2,5,6], so these types of materials will not be treated in the present book.

The book arose from discussions that took place during the FUNFLUOS project

(2004–2008), carried out within the Sixth European Framework Programme. This project

involved about ten groups from Germany, France, Slovenia and the UK, all aimed at the

synthesis and characterization of fluorinated materials with properties tailored for specific

applications.

The topics appearing in the book range from new synthesis routes to physical-chemical

characterizations. They address important properties of these materials, including morphol-

ogy, structure, thermal stability, superconductivity, magnetism, spectroscopic and optical

behaviour. Detailed ab initio investigations and simulations provide a comparison with

experimental results, and potential applications of the final products are also proposed.

In the first section, two innovative routes toward nanoscaled metal fluorides and

hydroxyfluorides are presented: the fluorolytic sol-gel synthesis by E. Kemnitz et al. and

the microwave-assisted route by D. Dambournet et al. In a second section, several

physical-chemical characterizations are developed in order to understand the mechanisms

that are responsible for the improvement of the properties of these materials: investigation

of the main characteristics of high-surface-area aluminium fluorides as catalysts by

E. Kemnitz and S. Rudiger; determination of surface acidities (Lewis and Brønsted

types) using a large range of probe molecules, by A. Vimont et al.; a better knowledge

of the environment of the different nuclei using high-resolution solid-state nuclear mag-

netic resonance (NMR) by C. Legein et al. The theoretical investigation of these topics is

highlighted by the predictive modelling of aluminium fluoride surfaces by C. Bailey et al.,

which allows a better understanding of the underlying processes at the molecular and nano

levels. An example of industrial application of the inorganic fluorides is given by P. Garcia

Juan et al. In the following section, some examples of outstanding optical properties of

nanostructured fluorides are proposed: nanostructured fluorocompounds as UV absorbers,

by A. Demourgues et al.; transparent oxyfluoride glass-ceramics by M. Mortier and

G. Dantelle; luminescent and antireflective coating of (oxy)fluorinated materials obtained

by the sol-gel technique, by S. Fujihara; planar optical waveguides based on fluoride

glasses, by B. Boulard. Hybrids, composites and mesoporous fluorides are original mate-

rials with great potential and the interesting nature of such materials is illustrated in

the next section by the chapters on polyanion condensation in inorganic-organic

hybrid fluorides, by K. Adil et al.; superconducting/magnetic properties of Cu-

and Mn-based oxyfluorides, by E. Antipov and A. Abakumov; ionic conductivity

of fluoride-containing phases by E. Ardashnikova et al.; intercalation in hybrid com-

pounds containing perfluoroalkyl groups, by Y. Matsuo.

The two following chapters deal with the synthesis of microporous frameworks using

the fluoride and F2-gas routes, respectively. The examples concern either compounds

based on silica, germanium, phosphates and clays, by J. L. Paillaud et al., or highly

fluorinated silica, by A. Demourgues et al. The optical and magnetic properties of

oxyfluoride glasses based on rare-earth elements are illustrated by S. Yonezawa et al.

Finally the chapter by A. Tressaud et al. describes the use of surface fluorination of porous

alumina for applications in offset technology.

A very wide range of materials, properties, and applications have therefore been

gathered in this book, which covers various new fields in which inorganic fluorides are

part of the innovating process. Among the information that can bring answers to some

crucial questions in materials science, we can quote new synthesis routes towards more

xviii Preface

efficient and less aggressive catalysts, protection against harmful UV radiation, new

integrated lasers and optical amplifiers, antireflective coatings, solid-state ionic conduc-

tors, highly hydrophobic silica and switchable coatings for offset technology.

Erhard Kemnitz and Alain Tressaud

Berlin and Bordeaux

September 2009

References

[1] Advanced Inorganic Fluorides, T. Nakajima, B. Zemva, A. Tressaud (Eds), Elsevier,Amsterdam (2000).

[2] Fluorinated Materials for Energy Storage, T. Nakajima, H. Groult (Eds), Elsevier, Amsterdam(2005).

[3] Fluorine and the Environment, Vol. 1 and Vol. 2, A. Tressaud (Ed.), Elsevier, Amsterdam(2006).

[4] Fluorine and Health, A. Tressaud and G. Haufe (Eds), Elsevier, Amsterdam (2008).[5] Graphite Fluorides and Carbon-Fluorine Compounds, T. Nakajima (Ed.), CRC Press, Boca

Raton, FL (1991).[6] ‘Fluorofullerenes’, in Dekker Encyclopedia of Nanoscience and Nanotechnology, O. V.

Boltalina, S. H. Strauss, 2nd edition, Dekker, New York (2009).

The Funfluos European Network (2004): First row (from left to right): D. Menz, B. Zemva,E. Kemnitz (Coordinator), A. Demourgues, A. Tressaud, and J. Winfield. Second row (from leftto right): U. Gross, M. Feist (partly hidden), S. Rudiger, P. Millet (European Commission),N. Harrison, A. Wander, T. Skapin and S. Schroder

Preface xix

List of Contributors

Artem M. Abakumov, Department of Chemistry, Moscow State, University, Moscow,

Russia

Karim Adil, Laboratoire des Oxydes et Fluorures, UMR CNRS, Le Mans, France

Evgeny V. Antipov, Department of Chemistry, Moscow State, University, Moscow,

Russia

Elena I. Ardashnikova, Department of Chemistry, Moscow State, University, Moscow,

Russia

Christine L. Bailey, Computational Science and Engineering Department, STFC

Daresbury Laboratory, Warrington, Cheshire, UK

Monique Body, Laboratoire de Physique de l’Etat Condense, UMR-CNRS, Universite der

Maine, Le Mans, France

Brigitte Boulard, Laboratoire des Oxydes et Fluorures, UMR CNRS, Le Mans, France

Jocelyne Brendle, Laboratoire de Materiaux a Porosite Controlee, UMR-CNRS,

Universite de Haute Alsace, Mulhouse, France

Jean-Yves Buzare, Laboratoire de Physique de l’Etat Condense, UMR-CNRS, Universite

der Maine, Le Mans, France

Amandine Cadiau, Laboratoire des Oxydes et Fluorures, UMR CNRS, Le Mans, France

Philippe Caullet, Laboratoire de Materiaux a Porosite Controlee, UMR-CNRS,


Damien Dambournet, Institute of Condensed Matter Chemistry of Bordeaux (ICMCB-

CNRS), University Bordeaux 1, Pessac, France

Geraldine Dantelle, Laboratoire de Photonique Quantique et Moleculaire (LPQM), UMR

CNRS, Cachan, France

Marco Daturi, ENSICAEN, Universite de Caen, CNRS, Caen, France

Alain Demourgues, Institute of Condensed Matter Chemistry of Bordeaux (ICMCB-


Etienne Durand, Institute of Condensed Matter Chemistry of Bordeaux (ICMCB-CNRS),

University Bordeaux 1, Pessac, France

Johannes Eicher, Solvay Fluor GmbH, Hannover, Germany

Shinobu Fujihara, Department of Applied Chemistry, Faculty of Science and

Technology, Keio University, Yokohama, Japan

Placido Garcia Juan, Solvay Fluor GmbH, Hannover, Germany

Nicholas Harrison, Computational Science and Engineering Department, STFC

Daresbury, Laboratory, Warrington, Cheshire, UK Department of Chemistry, Imperial

College London, London, UK

Annie Hemon-Ribaud, Laboratoiredes OxydesetFluorures, UMR CNRS, Le Mans, France

Erhard Kemnitz, Institute for Chemistry, Humboldt University of Berlin, Berlin,

Germany

Jae-ho Kim, Graduate School of Engineering, University of Fukui, Fukui, Japan

Ilya B. Kutsenok, Department of Chemistry, Moscow State, University, Moscow, Russia

Christine Labrugere, Institute of Condensed Matter Chemistry of Bordeaux (ICMCB-


Emilie Lataste, Institute of Condensed Matter Chemistry of Bordeaux (ICMCB-CNRS),


Marc Leblanc, Laboratoire des Oxydes et Fluorures, UMR CNRS, Le Mans, France

Christophe Legein, Laboratoire des Oxydes et Fluorures, CNRS, Le Mans, France

Vincent Maisonneuve, Laboratoire des Oxydes et Fluorures, UMR CNRS, Le Mans,

France

Charlotte Martineau, Laboratoire des Oxydes et Fluorures, UMR CNRS, Le Mans,

France, Tectospin, Universite de Versailles Saint Quentin en Yvelines, Versailles, France

Yoshiaki Matsuo, Department of Materials Science and Chemistry, University of Hyogo,

Hyogo, Japan

xxii List of Contributors

Michel Mortier, Laboratoire de Chimie de la Matiere Condensee de Paris, UMR CNRS,

Paris, France

Sanghamitra Mukhopadhyay, Department of Chemistry, Imperial College London,

London, UK

Jean-Louis Paillaud, Laboratoire de Materiaux a Porosite Controlee, UMR-CNRS,


Joel Patarin, Laboratoire de Materiaux a Porosite Controlee, UMR-CNRS, Universite de

Haute Alsace, Mulhouse, France

Nicolas Penin, Institute of Condensed Matter Chemistry of Bordeaux (ICMCB-CNRS),


Vladimir A. Prituzhalov, Department of Chemistry, Moscow State, University, Moscow,

Russia

Stephan Rudiger, Institute for Chemistry, Humboldt University of Berlin, Berlin,

Germany

Gudrun Scholz, Institute for Chemistry, Humboldt University of Berlin, Berlin,

Germany

Thomas Schwarze, Solvay Fluor GmbH, Hannover, Germany

Barry Searle, Computational Science and Engineering Department, STFC Daresbury

Laboratory, Warrington, Cheshire, UK

Gilles Silly, Institut Charles Gerhardt Montpellier, Physicochimie des Materiaux

Desordonnes et Poreux, Universite de Montpellier II, Montpellier, France

Angelique Simon-Masseron, Laboratoire de Materiaux a Porosite Controlee, UMR-

CNRS, Universite de Haute Alsace, Mulhouse, France

Laetitia Sronek, Institute of Condensed Matter Chemistry of Bordeaux (ICMCB-CNRS),


Hans-Walter Swidersky, Solvay Fluor GmbH, Hannover, Germany

Masayuki Takashima, Graduate School of Engineering, University of Fukui, Fukui,

Japan

Alain Tressaud, Institute of Condensed Matter Chemistry of Bordeaux (ICMCB-CNRS),


List of Contributors xxiii

Alexandre Vimont, ENSICAEN, Universite de Caen, CNRS, Caen, France

Adrian Wander, Computational Science and Engineering Department, STFC Daresbury

Laboratory, Warrington, Cheshire, UK

John M. Winfield, Department of Chemistry, University of Glasgow, Glasgow, UK

Susumu Yonezawa, Graduate School of Engineering, University of Fukui, Fukui, Japan

xxiv List of Contributors

1

Sol-Gel Synthesis of Nano-ScaledMetal Fluorides – Mechanism and

Properties

Erhard Kemnitz, Gudrun Scholz and Stephan Rudiger

Humboldt-Universitat zu Berlin, Institut fur Chemie, Brook – Taylor – Str. 2,

D – 12489 Berlin, Germany

1.1 Introduction

Sols are dispersions of nanoscopic solid particles in, for example, liquids – i.e., colloidal

solutions. The particles can agglomerate forming a three-dimensional network in the

presence of large amounts of the liquid thus forming a gel. Inorganic sols are prepared

via the sol-gel process, the investigation of which started in the nineteenth century. This

process received great impetus from the investigations of Stober et al. [1], who studied the

use of pH adjustment on the size of silica particles prepared via sol-gel hydrolysis of tetra-

alkoxysilanes.

1.1.1 Sol-Gel Syntheses of Oxides – An Intensively Studied and Widely Used Process

Hydrolysis of alkoxysilanes and later on of metal alkoxides in organic solutions has

become an intensively studied and widely used process [2]. The most common products

are almost homodispersed nanosized silica or metal oxide particles for, e.g., ceramics or

Functionalized Inorganic Fluorides: Synthesis, Characterization & Properties of Nanostructured Solids Edited by Alain Tressaud

� 2010 John Wiley & Sons, Ltd

glasses, or the aqueous sols are used to prepare different coatings for, e.g., optical

purposes. Optical applications depend on differences in the respective indices of refraction

of the coated material and the applied layer. The latter has to be of very uniform and

thoroughly adjusted thickness.

The sol-gel hydrolysis of alkoxysilanes, the most intensively explored one, basically

proceeds in two steps. The first step is the hydrolytic replacement of alkoxy groups, OR, by

hydroxyl groups, OH, shown schematically in Equation (1.1) for the first alkoxy group:

SiðORÞ4 þH2O ! ðROÞ3SiOH þ ROH (1:1)

Because of their relatively high hydrolytic stability, hydrolysis of alkoxysilanes (1.1)

has to be catalysed by Brønstedt acids or bases.

In the second step, the primary hydrolysis products undergo condensation reactions

under elimination of water (Equation (1.2)) or alcohol (Equation (1.3)).

X3Si-OH þ HO-SiX3 ! X3Si-O-SiX3 þH2OðX¼OR; OHÞ (1:2)

X3Si-OH þ RO-SiX3 ! X3Si-O-SiX3 þ ROHðX¼OR; OHÞ (1:3)

As a result tiny particles with a very open structure are formed. The overall process can

be controlled by adjusting the reaction conditions. The colloidal solution of these

particles, the sol, can be used as such for, e.g., coating or it can be worked up to yield,

eventually, nanoscopic oxide particles. However, metal oxide sols obtained in this way

always contain a sometimes remarkable organic part. Its separation demands calcination

temperatures of at least 623 K in order to convert the ‘precursors’ into pure metal oxide

materials.

Substituting a certain part of the alkoxidic groups by nonhydrolysable ones, such as

alkyl groups in the case of alkoxysilanes or phosphonic acid in the case of metal alkoxides,

organically modified oxides, i.e. inorganic-organic hybrid materials, have been prepared.

1.1.2 Sol-Gel Syntheses of Metal Fluorides – Overview of Methods

Selected metal fluorides can, in application-relevant fields, outperform metal oxides and

silica. Thus, for instance, magnesium fluoride and aluminium fluoride and, in particular,

alkali hexafluoroaluminates have both a lower index of refraction and a much broader

spectral range of transparency even than silica, making them very interesting for optical

layers.

Consequently, several approaches for the preparation of nanoscopic metal fluorides and

metal fluoride thin layers have been developed and proposed. Besides physical methods

such as milling, laser dispersion or molecular-beam epitaxy, different chemical methods

exist. Basically, three approaches can be distinguished:

(i) Postfluorination of a metal oxide preformed via sol-gel route [3].

This route is shown schematically in Scheme 1.1. The disadvantages of this route are, to

name two, incomplete fluorination of the bulk metal oxides and decrease of surface area in

course of the fluorination.

2 Functionalized Inorganic Fluorides

(ii) Preparation of a precursor containing a metal compound with organically bound

fluorine such as trifluoroacetate, which is calcined to decompose the fluoroorganic

component under formation of metal fluoride [5].

This route, shown in Scheme 1.2, also starts from metal alkoxides, which are reacted in

solution with, e.g., trifluoroacetic acid to form metal trifluoroacetate sol. This can be

M(OR)x + xH2O MOx/2 (sol) + xROH

hydrolysis coating

MOx/2(gel) bulk MOx/2(gel) film

fluorination+

calcination

fluorination

MFx or MOx/2/MFx glass MFx or MOx/2/MFx film

Scheme 1.1 Metal fluoride preparation via post fluorination of sol-gel prepared metal oxides(Reproduced from [4] by permission of Elsevier Publishers)

metal trifluoroacetate (TFA) precursor solution

M(OR)x and/or MOAc + CF3COOH + H2O + org. solvent

drying coating

metal-TFA(gel) bulk metal-TFA(gel) film

heating

metal fluoride powder metal fluoride film

heating at higher temperature

MOx/2/MFx powder MOx/2/MFx film

heating

Scheme 1.2 Metal fluoride preparation via metal fluoroacetate sol-gel formation and followingthermal decomposition. (Reproduced from [4] by permission of Elsevier Publishers)

Sol-Gel Synthesis of Nano-Scaled Metal Fluorides – Mechanism and Properties 3

used for coating experiments. The decisive final step is the thermal decomposition of the

fluoro-organic constituent, because of which thermolabile materials cannot be coated.

Another disadvantage is the probability that oxidic components can be formed as admix-

tures or oxofluorides.

(iii) Fluorolytic sol-gel process as counterpart to the hydrolytic one.

The fluorolytic sol-gel route follows rather strictly the ‘classical’ hydrolytic one by

reacting metal alkoxides in anhydrous solution with hydrogen fluoride instead of the

hydrogen oxide of the ‘classical’ process. Consequently, it results eventually in metal

fluorides instead of metal oxides.

The fluorolytic sol-gel process, its execution, mechanism, scope as well as properties

and possible fields of application of its products are the subjects of this chapter.

1.2 Fluorolytic Sol-Gel Synthesis

Metal alkoxides can be regarded as metal salts of alcohols, where the latter are very weak

Brønstedt acids. Acids that are stronger than the respective alcohol can therefore replace

alkoxy groups attached to the metal ion under liberation of the alcohol and formation of the

metal fluoride according to Equation (1.4).

MðORÞn þ x HF ! MðORÞn�xFx þ x ROH ðM¼metal ionÞ (1:4)

In fact, starting with aluminium isopropoxide [6], a broad range of metal alkoxides have

been subjected to a sol-gel-like liquid-phase fluorination with hydrogen fluoride in organic

solution [4, 7]. Although Equation (1.4) closely resembled Equation (1.1) there is an

important difference in that condensation reactions like those of Equations (1.2) and

(1.3) are not possible in the fluorolysis system. On the other hand, the fluorolysis reactions

typically result in the formation of a sol-gel. The formation of a gel was already mentioned

in the first paper on metal alkoxide fluorolysis, reporting the reaction of aluminium

isopropoxide in alcoholic solution with an ethereal solution of hydrogen fluoride [6].

The gel formation is obviously due to an important consequence of the replacement of

alkoxy groups by fluoride, i.e., the Lewis acidity of the metal ion increases leading to a

strengthening of the interaction between (liberated) alcohol molecules and metal ions. As a

result alcohol molecules that can occupy ligand positions might establish a loose net

between (partly) fluorinated metal ions resulting eventually in metal fluoride sol or even

gels. Surprisingly, attempts to isolate pure AlF3 by drying and calcining the gel were not

successful; the product obtained had an understoichiometric amount of fluorine even when

the primary reaction has been carried out with an overstoichiometric amount of HF [8]. An

additional fluorination of the dried gel under gentle conditions (see below) has proved to

be a suitable way to remove the attached organic components resulting in X-ray amor-

phous, highly Lewis acidic aluminium fluoride with unusual large specific surface area,

named HS-AlF3 [9].

4 Functionalized Inorganic Fluorides

functionalized inorganic fluorides · functionalized inorganic fluorides: synthesis,...

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